In the standard for coding audiovisual objects according to MPEG-4, in ISO/IEC 14496-3 FCD, Subpart 2, parametric coders are specified, in particular the HVXC (Harmonic Vector Excitation Coding) coder, for coding speech at extremely low bitrates. In order to generate the LPC coefficients, the spectral envelopes of the speech signal, and the unvoiced segments, this standard contains a plurality of tables that are present in floating-point format.
In Subpart 3 of this standard, the CELP (Code Excited Linear Prediction) coder for coding speech at medium to low bitrates is described. For generating the LPC coefficients and the gain values, this standard contains a plurality of tables that are present in floating-point format.
For coding such speech signals, the method of “analysis through synthesis” is often used (ANT Nachrichtentechnische Berichte, Heft 5, November 1988, pages 93 to 105). In the mentioned speech coding methods, values are stored in code books, i.e., in the tables, the values being used for the generation of the signal parameters and thus for the coefficients of the speech synthesis filter. The values stored in the code books are read out via an index control unit.